Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
In several geographies water shortage is becoming a more and more acute problem and this is particularly true in developing countries.
Household cleaning processes like washing laundry, dishes etc, require large amounts of water. It will be a great benefit to the society if it will be possible to save this water and also reuse the water used in such activities. The water generated in-home from washing and rinsing laundry is generally referred to as grey water. In order to reuse such household grey water for various activities it is essential to remove all the particulate matter and the surfactants.
Several water purification processes using chemicals such as flocculants and coagulants especially for making water safe for drinking are known in the art. There are also several techniques to purify industrial waste water. Most of these methods involve use of chemicals like aluminium salts and polymers which have an adverse effect on the environment.
WO2002000557 (P&G) describes a water purification composition comprising essentially a primary coagulant, a bridging flocculent, a coagulant aid and optionally a disinfectant. This patent application also claims a method for clarifying and purifying water, which comprises several stages selected from coagulation and flocculation, disinfection, filtration, neutralisation and fortification.
EP1953119 (Unilever) describes solid water purification composition in the form of a two-component system, with a first component comprising a biocide and a water-insoluble adsorbent, and a second component comprising a coagulating agent and a flocculating agent. A biocide quencher may be included in the composition.
WO2012084621 (Unilever), discloses a fast water purification and clarification process for the treatment of household water, especially laundry wash and more typically laundry rinse water by using a composition comprising flocculant, coagulant, filler and cationic surfactant, effective for water clarification and purification.
A device and a process for purification of grey water, especially grey water generated in household processes such as laundry wash and rinse water without the addition of chemicals is highly desired and is beneficial to the environment. The present inventors have been able to develop a device and physical process for purification of grey water especially for in-home purification, which process does not require the addition of chemicals like aluminium salts and polymers that have an adverse effect on the environment.
Goldberg and Rubin (I & EC Process Design and Development, 1967, Vol 6) disclose process of mechanical foam breaking by the shearing action of a high speed rotating disc. However it only discloses foam flow rates upto 200 ml/min by using a smooth disc rotating at a speed of about 2500 rpm. The surfactant used in the process was Triton X-100 which is not a very high foaming surfactant and at relatively low concentrations. They also had a limitation on the disc speed because as the disc speed was increased larger amount of liquid was carried with the foam. This will result in poor recovery of purified water. It does not disclose how the remove foam from the grey water by only channelling the foam while substantially preventing the liquid from getting channelled, which will help in collecting most of the grey water as purified water.
Andou S et al., (Performance characteristics of mechanical foam breakers with rotating parts fitted to bubble column, J. of chem. tech. and biotech, vol 68, no. 1, 1 January, 1997, pg 94-100), compares mechanical foam breakers shaped like fans with vanes/blades oriented perpendicular to the plane rotation with the “blades” in various orientations. These foam breakers, not only consume more power, but also cause a fine mist of droplets in the exhaust air and the liquid phase of the foam gets scattered into a mist which is carried with the air-flow stream leaving the foam breaker. Thus the recovery and collection of pure water from grey water is low.
The present inventors have been able to develop a device and a process to purify grey water which is generated from laundry wash and/or rinse liquor that has high foaming surfactants at relatively high concentrations. Efficient purification of grey water has been achieved by generating and breaking foam using flow rates of 20,000-50,000 mL/min ensuring that the foam is sufficiently dry when it reaches the foam breaking device having a rotating disc whose surface has a patterned roughness.
Surprisingly in the present invention it was found that it is possible to design a device and a process where, by continuous aeration, more than 90% of the surfactant present in used laundry water can be transferred into foam. If the foam is then allowed to channel out from the chamber holding the grey water, and made to collapse outside the chamber, a device and process can be built to remove dissolved surfactants from water. It is thus possible to recover more than 90% of grey water as purified water even when the surfactant level in the grey water is as high as 0.1%. The recovered purified water preferably can be subsequently passed through at least one filter to get further purified water. The key step in achieving the above is the ability to cause foam collapse at very high volumetric flow rate of the foam. It is an object of the invention to provide a device for purification of grey water.
It is another object of the present invention to provide a device for purification of grey water generated in household process, especially laundry wash and rinse processes without the addition of chemicals that have an adverse effect on the environment.
It is another object of the present invention where the surfactant level of the grey water is reduced to less than 1 ppm.
It is another object of the invention to provide a simple physical process for purification of grey water where more than 90% recovery of purified water can be achieved.